The present invention relates to a light modulating device including a waveguide structure, and more particularly a light modulating device array suitable for use in an optical information generating apparatus such as a laser printer.
A conventional light modulating device usually includes only one light modulating part. FIG. 2 shows the conventional light modulating device. Referring to FIG. 2, optical waveguides 1, 2, 3 and 4 are formed by diffusing titanium in the surface of a LiNbO.sub.3 crystal 7, and a laser beam 9 is directed to the optical waveguide 1 through a lens 8. Light having passed through the optical waveguide 1 is divided into two parts, which pass through the optical waveguides 2 and 3. In other words, the optical waveguide 1 is bifurcated at the end thereof. Light beams having passed through the optical waveguides 2 and 3 are combined by the optical waveguide 4, that is, the optical waveguides 2 and 3 meet each other at the head of the optical waveguide 4. The combined light beam passes through the optical waveguide 4, and then leaves the crystal 7. When the length of the optical guide 2 between the end of the optical waveguide 1 and the head of the optical waveguide 4 is made equal to that of the optical waveguide 3, the light beams having passed through the optical waveguides 2 and 3 are in phase with each other at the head of the optical waveguide 4, and thus a laser beam emerges from the crystal 7 with a strong intensity. Electrodes 5 and 6 are provided on the optical waveguides 5 and 6, respectively. When a voltage is applied between the electrodes 5 and 6, an electric field is established in the crystal 7 between the electrodes 5 and 6 so that the electric field at the optical waveguides 2 and 3 is perpendicular to the surface of crystal 7, that is, parallel or anti-parallel to a Z-direction, and the direction of the electric field at the optical waveguide 2 is opposite to the direction of the electric field at the optical waveguide 3. Accordingly, when the crystal 7 is a Z-cut plate of LiNbO.sub.3, the electrooptic constant r.sub.33 having a large value is utilized, and the phase difference between two light beams at the head of the optical waveguide 4 can be made equal to .pi. (namely, 180.degree.) by applying a relatively low voltage between the electrodes 5 and 6. When the phase difference at the head of the optical waveguide 4 is made equal to .pi. as mentioned above, the combined light beam becomes weak as a result of interference of two light beams. The conventional light modulating device can modulate incident light in the manner mentioned above, and thus is considered to be a light modulating device provided with a Mach-Zehnder type waveguide structure. As has been already mentioned, the conventional light modulating device includes only one light modulating part. When a plurality of light modulating devices each corresponding to the conventional device are combined to form an array, there arise the following problems. That is, it is not easy to impart incident light efficiently to a plurality of light modulating parts. Further, the leakage of an electric field from a light modulating part supplied with a voltage to another light modulating part adjacent thereto may cause a false operation.